AwkwardPotato

Agreed with the others on replacing the caps. I doubt that the keyboard is the issue; there are different components in the soft power circuit for both powering on and powering off.

I believe the earliest 128k's used a black plastic sheet behind the analog board as opposed to the white one with red lettering that's normally found in Compacts.

The glue on that flyback looks pretty burnt, so I wouldn't be surprised if it's bad. The Dead Mac Scrolls also suggests that the flyback and/or horizontal output transistor are dead. Also, just because the caps look good doesn't necessarily mean they are good.

One of the leads on the AT&T DSP already looks like it's being eaten by the cap goo, although that's probably not the cause of your boot issue. Even if you aren't able to recap the board immediately, it would be a good idea to wash it as soon as possible to prevent more damage.

The IIGS's standard RAM is comprised of 4x 150ns TMS4464 ICs. Compatible parts can be found on eBay, just make sure the number after the hyphen (which indicates the speed) is less than or equal to 15.

Definitely recap it while it still shows some signs of life. The Q840av is notoriously difficult to revive once the damage is too far gone.

Yeah, it looks like the errors are 8 pixels apart from each other. The IIGS stores 4 pixels to a byte in this mode though and it doesn't look like entire groups of 4 pixels are wrong, so it might not be an addressing problem. You could try replacing the Standard RAM, and also reseating the VGC. If you do reseat the VGC, don't try prying it out of the socket with a screwdriver as the sockets are very fragile and will crack. You can buy PLCC extractors on Amazon/eBay for this purpose.

Replacement orange Alps can be had here on eBay for around $6 shipped. The Matias ones will work fine, but they might feel a bit out-of-place compared to the other switches in the keyboard.

Maybe there's a corroded trace on the LCD's PCB?

The CRT doesn't always implode if you break it. Usually you'll just hear a faint hissing sound as air fills the tube.

As Jinnai says, there are two types of yo-yo adapters. The one that'll work on the 1400 has a clear connector on the computer side, as opposed to the later one which has a translucent black connector (here's an example of a compatible one on eBay). All of the PowerBook G3 black bricks that preceded the yo-yo's will work fine too. The white square ones that came with the white iBook G3s will not work, however.

I know you can get aftermarket 1400 power adapters on eBay from China that are supposedly compatible, but personally I don't really trust those. Don't limit yourself to just looking for a 1400 adapter though, the PowerBook G3's used a compatible adapter (some of the iBook "yo-yo" ones were compatible but some aren't).

Awesome haul! I don't have any spares, but I can measure the ones in my IIx so you can find new ones, if you want.

Jeez, I'm sorry. I should've remembered to mention not to do that when I linked the image from his site.

They both use practically the same board, so yes, the RAM will fit.